Commitments and Contingencies - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) ft² Agreement Subsidiary	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Non-cancelable leases expiration date	Dec. 31, 2034
Rental expense	$ 13.1	$ 5.3	$ 4.0
Rent abatement and concessions	$ 11.5	2.7
Number of lease agreements assigned to third parties | Agreement	2
Future lease obligation under sublease arrangements	$ 5.8
Number of subsidiaries | Subsidiary	2
Settlement days of bond transaction	Within one to two trading days
Collateral deposits	$ 1.1	$ 1.2
Property One [Member]
Loss Contingencies [Line Items]
Lease termination dates	2020-11
Property Two [Member]
Loss Contingencies [Line Items]
Lease termination dates	2022-02
Lease Agreement [Member]
Loss Contingencies [Line Items]
Newly built office space | ft²	83,000
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Contingent obligation for standby letter of credit issued to Landlord	$ 1.7